The present invention relates to a toothed mobile part such as a wheel, pinion, or rack for a gear, particularly in horology.
It is known that in timepieces such as wristwatches, gear backlash detracts from the display precision. In the case of an eccentric hand, for example, gear backlash may cause the hand to quaver under the effect of movements of the user. In displays with a retrograde hand, such as for indication of the equation of time, the hand may start to move in the other direction only when the plays have been taken up, a certain time after inversion of the movement of the gear train driving it. The plays of gears may accumulate within a given gear train. Plays therefore are so much more important and detrimental the more gears exist in the gear train.
Toothed mobile parts allowing the play of a gear to be taken up have been described in patent applications WO 2004/008004, EP 1,555,584, and EP 1,744,081. These mobile parts have teeth that are larger than normal teeth in order to reduce the space between any two consecutive teeth, and thus to reduce or eliminate the play, but may become deformed or move elastically in the case of gripping in order to avoid gear blocking. The elastic deformation or mobility of the teeth is obtained by slots and/or hollows machined into the teeth or into the plate of the mobile part. In certain embodiments proposed, the teeth consist of a rigid segment and an elastic segment that may lean against the rigid segment in the case of gripping. In other embodiments the teeth consist of two elastic segments that may lean against each other. In still other embodiments, the teeth are rigid but linked elastically through flexible blades to the plate of the mobile part. In an embodiment illustrated in FIG. 9 of document EP 1,555,584, every other tooth has a rigid segment and an elastic segment, the remaining teeth are fixed and entirely rigid.
It is a disadvantage of the toothed mobile parts for the takeup of play that have been mentioned above, that they are only able to take up a relatively slight play, because the elastic segments of the teeth have small dimensions and during gripping of the gear must rapidly come up against a rigid segment in order not to overstep their elastic limit.